Dust from giant asteroid crash caused ice age 466 million years ago and boosted biodiversity on Earth
Dust from a gigantic asteroid breakup triggered an ice age 466 million years ago and sparked a burst of marine biodiversity on Earth, new research has revealed.
Long before the age of the dinosaurs, the Earth froze, and the seas began to ice over at the Earth's poles. The new range of temperatures around the planet set the stage for new species to evolve. While the cause of this ice age had been a mystery, new research - by an international team led by Lund University, Sweden - shows that the ice age was caused by global cooling, triggered by extra dust in the atmosphere from a giant asteroid collision in outer space.
During the extraterrestrial event that formed life on Earth, a 150 km asteroid (an illustration is shown in the image above; Don Davis, Southwest Research Institute) was crushed between Jupiter and Mars and the dust spread through the solar system, leading to a unique ice age and, subsequently, to higher levels of biodiversity.
"Our results show for the first time that such dust, at times, has cooled Earth dramatically," says Birger Schmitz from Sweden's Lund University, the study's lead author and a research associate at the Field Museum.
In limestone found in Russia and Sweden, scientists detected extraterrestrial material in sediments deposited almost half a billion years ago that suggests the asteroid breakup. This event took place at the same time as a major fall in sea level that is frequently attributed to onset of a mid-Ordovician ice age.
"The blocking effect of the dust partially stopped sunlight reaching Earth, and an ice age began. The climate changed from being more or less homogeneous to becoming divided into climate zones - from Arctic conditions at the poles to tropical conditions at the equator. The high diversity among invertebrates came as an adaptation to the new climate, triggered by the exploded asteroid," says the study published in Science Advances.
It further says, "An important method that led to the discovery was the measurements of extraterrestrial helium incorporated in the petrified sea floor sediments at Kinnekulle in southern Sweden. On its way to Earth, the dust was enriched with helium when bombarded by the solar wind."
According to the researchers, there is always a lot of dust from outer space floating down to Earth, little bits of asteroids and comets, but this dust is normally only a tiny fraction of the other dust in the atmosphere such as volcanic ash, dust from deserts and sea salt. "But when a 93-mile-wide asteroid between Mars and Jupiter broke apart 466 million years ago, it created way more dust than usual. Normally, Earth gains about 40,000 tons of extraterrestrial material every year. Imagine multiplying that by a factor of a thousand or ten thousand," says the study.
The research team looked for traces of space dust in 466-million-year-old rocks and compared it to tiny micrometeorites from Antarctica as a reference. "We studied the extraterrestrial matter, meteorites, and micrometeorites, in the sedimentary record of Earth, meaning rocks that were once seafloor. We then extracted the extraterrestrial matter to discover what it was and where it came from," says one of the paper's authors, Philipp Heck, a curator at the Field Museum and an associate professor at the University of Chicago.
The researchers suggest that the large amounts of extraterrestrial dust over a timeframe of at least two million years played an important role in changing the climate on Earth, contributing to cooling. They explain since the dust floated down to Earth over at least two million years, the cooling was gradual enough for life to adapt and even benefit from the changes. An "explosion of new species evolved" as creatures adapted for survival in regions with different temperatures.
The "unexpected discovery," says the research team, could be relevant for tackling global warming if we fail to reduce carbon dioxide emissions.
Scientists over the last decade or so have discussed different artificial methods to cool the Earth in case of a major climate catastrophe. Modelers have shown that it could be possible to place asteroids, much like satellites, in orbits around Earth in such a way that they continuously liberate fine dust and hence partly block the warming sunlight.
"Our studies can give a more detailed, empirical-based understanding of how this works, and this, in turn, can be used to evaluate if model simulations are realistic," says Schmitz.
The researchers say while this period of global cooling proved beneficial to life on Earth, fast-paced climate change can be catastrophic. "In the global cooling we studied, we are talking about timescales of millions of years. It is very different from the climate change caused by the meteorite 65 million years ago that killed the dinosaurs, and it is different from global warming today. This global cooling (the one mentioned in the study) was a gentle nudge, there was less stress," says Heck.
According to the research team, while it could be tempting to think that the present-day global warming could be solved by replicating the dust shower that caused global cooling 466 million years ago, they say scientists must be cautious and must evaluate geoengineering proposals critically.
While Heck is not convinced that scientists have found the solution to climate change, he says it could be a good idea to think along these lines. "We are experiencing global warming. We need to think about how we can prevent catastrophic consequences or minimize them. Any idea that is reasonable should be explored," he adds.